Thermo-compression bonded electrical interconnect structure

ABSTRACT

An electrical structure and method for forming. The electrical structure includes a first substrate comprising a first electrically conductive pad, a second substrate comprising a second electrically conductive pad, and an interconnect structure electrically and mechanically connecting the first electrically conductive pad to the second electrically conductive pad. The interconnect structure comprises a non-solder metallic core structure and a first solder structure. The first solder structure electrically and mechanically connects a first portion of the non-solder metallic core structure to the first electrically conductive pad. A second portion of the non-solder metallic core structure is thermo-compression bonded to the second electrically conductive pad.

This application is a divisional application claiming priority to Ser.No. 11/855,290, filed Sep. 14, 2007.

FIELD OF THE INVENTION

The present invention relates to a thermo-compression bonded electricalinterconnect structure and method for forming.

BACKGROUND OF THE INVENTION

Connections between structures are typically unreliable and subject tofailure. Accordingly, there exists a need in the art to overcome atleast one of the deficiencies and limitations described herein above.

SUMMARY OF THE INVENTION

The present invention provides an electrical structure comprising:

a first substrate comprising a first electrically conductive pad;

a second substrate comprising a second electrically conductive pad; and

an interconnect structure electrically and mechanically connecting saidfirst electrically conductive pad to said second electrically conductivepad, wherein said interconnect structure comprises a non-solder metalliccore structure and a first solder structure in direct mechanical contactwith a first portion of said non-solder metallic core structure, whereinsaid first solder structure electrically and mechanically connects saidfirst portion of said non-solder metallic core structure to said firstelectrically conductive pad, and wherein a second portion of saidnon-solder metallic core structure is thermo-compression bonded to saidsecond electrically conductive pad.

The present invention advantageously provides a simple structure andassociated method for forming connections between structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross sectional view of an electrical structure, inaccordance with embodiments of the present invention.

FIG. 2 depicts a first alternative to FIG. 1, in accordance withembodiments of the present invention.

FIG. 3 depicts a first alternative to FIG. 2, in accordance withembodiments of the present invention.

FIG. 4 depicts a first alternative to FIG. 3, in accordance withembodiments of the present invention.

FIG. 5A depicts a first alternative to FIG. 4, in accordance withembodiments of the present invention.

FIG. 5B depicts a first alternative to FIG. 5A, in accordance withembodiments of the present invention.

FIG. 6A depicts a second alternative to FIG. 5A, in accordance withembodiments of the present invention.

FIG. 6B depicts a first alternative to FIG. 6A, in accordance withembodiments of the present invention

FIGS. 7A-7G illustrate a process for generating the electrical structure2C of FIG. 3 and/or the electrical structure of FIG. 4, in accordancewith embodiments of the present invention.

FIGS. 8A-8E illustrate a process for generating the electrical structureof FIG. 1 and/or the electrical structure of FIG. 2, in accordance withembodiments of the present invention.

FIGS. 9A-9E illustrate a process for generating the electrical structureof FIGS. 5A-6B, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cross sectional view of an electrical structure 2a, in accordance with embodiments of the present invention. Electricalstructure 2 a comprises a substrate 1, a substrate 4, a plurality ofinterconnect structures 5, an optional layer of adhesive 22, and anoptional layer(s) 16 of underfill encapsulant material. Substrate 1comprises a plurality of electrically conductive pads 10. Each pad ofelectrically conductive pads 10 may be connected to wires or electricalcomponents within substrate 1. Substrate 4 comprises a plurality ofelectrically conductive pads 12. Each pad of electrically conductivepads 12 may be connected to wires or electrical components withinsubstrate 4. Substrate 1 may comprise, inter alia, a semiconductordevice (e.g., an integrated circuit chip, a semiconductor wafer, etc), achip carrier (organic or inorganic), a printed circuit board, etc.Substrate 4 may comprise, inter alia, a semiconductor device (e.g., anintegrated circuit chip, a semiconductor wafer, etc), a chip carrier(organic or inorganic), a printed circuit board, etc. Each interconnectstructure 5 comprises a non-solder metallic (i.e., does not comprise anysolder material) core structure 5 and a solder structure 14. Solderstructure 14 comprises solder. Solder is defined herein as a metal alloycomprising a low melting point (i.e., about 100 degrees Celsius to about340 degrees Celsius) that is used to join metallic surfaces togetherwithout melting the metallic surfaces. Each solder structure 14comprises a portion of solder electrically and mechanically connecting abottom side 19 of non-solder metallic core structure 5 to electricallyconductive pad 12. Each non-solder metallic core structure 14 maycomprise any conductive metallic material that does not comprise solderincluding, inter alia, copper, gold, nickel, etc or any combinationthereof. Each interconnect structure 5 comprises a first non-soldermetallic structure 5 a and a second non-solder metallic structure 5 belectrically and mechanically connected to the first non-solder metallicstructure 5 a. First non-solder metallic structure 5 a may comprise afirst metallic material (e.g., gold) and second non-solder metallicstructure 5 b may comprise a second and different (i.e., from the firstmaterial) metallic material (e.g., copper). Alternatively, eachinterconnect structure 5 may comprise only a single non-solder metallicstructure (e.g., all copper). Each interconnect structure 5 isthermo-compression bonded (i.e., a bond is formed by using a heating andpressure process in order to form a bond) to an associated electricallyconductive pad 10. Each electrically conductive pad 10 may comprise afirst material layer 10 a (e.g., comprising a same material a comprisedby first non-solder metallic structure 5 a) formed over a secondmaterial layer 10 b (e.g., comprising a same material a comprised bysecond non-solder metallic structure 5 b). Additionally, each secondmaterial layer 10 b may comprise a plurality of material layers such as,inter alia, titanium/copper, chromium/copper, titanium/nickel,vanadium/copper, etc. The thermo-compression bond is formed betweenfirst material layer 10 a and first non-solder metallic structure 5 a.Each interconnect structure 5 electrically and mechanically connects anelectrically conductive pad 10 to an electrically conductive pad 12.Non-solder metallic core structure 5 comprises a cylindrical shape.Solder structure 14 may comprise any solder material suitable for a flipchip interconnections including, inter alia, an alloy of tin such asSnCu, SnAgCu, SnPb, etc. As an alternative, at least a first ofnon-solder metallic core structures 5 could be replaced by a solderstructure such that at least one of electrically conductive pads 10 isconnected to an associated electrically conductive pad 12 using anon-solder metallic core structure 5 and at least another ofelectrically conductive pads 10 is connected to an associatedelectrically conductive pad 12 using a solder structure.

FIG. 2 depicts a first alternative to FIG. 1 illustrating across-sectional view of an electrical structure 2 b, in accordance withembodiments of the present invention. In contrast with electricalstructure 2 a of FIG. 1, electrical structure 2 b of FIG. 2 eachinterconnect structure 5 d is thermo-compression bonded (i.e., a bond isformed by using a heating and pressure process in order to form a bond)to an associated electrically conductive pad 12 instead of soldered.Each interconnect structure 5 d comprises a first non-solder metallicstructure 5 a, a second non-solder metallic structure 5 b electricallyand mechanically connected to the first non-solder metallic structure 5a, and a third non-solder metallic structure 5 c electrically andmechanically connected to the second non-solder metallic structure 5 b.First non-solder metallic structure 5 a and third non-solder metallicstructure 5 a may comprise a first metallic material (e.g., gold) andsecond non-solder metallic structure 5 b may comprise a second anddifferent (i.e., from the first material) metallic material (e.g.,copper). Alternatively, each interconnect structure 5 d may compriseonly a single non-solder metallic structure (e.g., copper). Eachelectrically conductive pad 12 may comprise a first material layer 12 a(e.g., comprising a same material a comprised by third non-soldermetallic structure 5 c) formed over a second material layer 12 b (e.g.,comprising a same material a comprised by second non-solder metallicstructure 5 b). The thermo-compression bond is formed between firstmaterial layer 12 a and third non-solder metallic structure 5 c. Eachinterconnect structure 5 c electrically and mechanically connects anelectrically conductive pad 10 to an electrically conductive pad 12.

FIG. 3 depicts a first alternative to FIG. 2 illustrating across-sectional view of an electrical structure 2C, in accordance withembodiments of the present invention. Electrical structure 2C maycomprise an optional layer(s) 16 of underfill encapsulant material. Incontrast with electrical structure 2B of FIG. 2, electrical structure 2Cof FIG. 3 comprises a plurality of spherical interconnect structures 17comprising a spherical non-solder (i.e., does not comprise any soldermaterial) metallic core structure 17. Each non-solder (i.e., does notcomprise any solder material) metallic core structure 17 comprises a nonsolder metallic layer 17 b (i.e., comprising a first metallic materialsuch as, inter alia, gold) that completely surrounds an exterior surfaceof an associated non-solder metallic core 17 a (i.e., comprising asecond metallic material such as, inter alia, copper). Each non soldermetallic layer 17 b may comprise, inter alia, copper, gold, nickel, etc.Each non-solder metallic core 17 a may comprise, inter alia, copper,gold, nickel, etc. Alternatively, each non-solder metallic corestructure 17 may comprise a single non-solder metallic material such as,inter alia, copper. Each interconnect structure 17 comprises a firstportion 44 a thermo-compression bonded (i.e., comprising athemo-compression bond 40 a) to electrically conductive pad 10 and asecond portion 44 b thermo-compression bonded (i.e., comprising athemo-compression bond 40 b) to electrically conductive pad 12 therebyelectrically and mechanically connecting electrically conductive pad 10to electrically conductive pad 12. For first level area arrayinterconnects, each non-solder metallic core structure 17 may comprise adiameter of about 25 microns to about 150 microns. For second level areaarray interconnects (e.g., a ball grid array (BGA)), each non-soldermetallic core structure 17 may comprise a diameter of about 0.2 mm toabout 1.5 mm. Each non-solder metallic core structure 17 may comprise acore of any conductive metallic material that does not comprise solderincluding, inter alia, copper, gold, nickel, etc. Additionally, eachnon-solder metallic core structure 17 may comprise an additionallayer(s) of non-solder metallic materials (i.e., different from amaterial comprised by non-solder metallic core structure 17) surrounding(e.g., see layer 19 in FIG. 3, infra) non-solder metallic core structure17. The additional layer(s) may comprise any conductive metallicmaterial including, inter alia, nickel, gold, tin, etc.

FIG. 4 depicts a first alternative to FIG. 3 illustrating across-sectional view of an electrical structure 2D, in accordance withembodiments of the present invention. In contrast with electricalstructure 2C of FIG. 3, electrical structure 2D of FIG. 3 comprisessolder structures 25. Solder structure 25 comprises solder. Solder isdefined herein as a metal alloy comprising a low melting point (i.e.,about 100 degrees Celsius to about 340 degrees Celsius) that is used tojoin metallic surfaces together without melting the metallic surfaces.Each solder structure 25 comprises a portion of solder electrically andmechanically connecting a portion 27 of non-solder metallic corestructure 17 to an associated electrically conductive pad 12. As analternative, at least a first of non-solder metallic core structures 17could be replaced by a solder structure such that at least one ofelectrically conductive pads 10 is connected to an associatedelectrically conductive pad 12 using a non-solder metallic corestructure 17 and at least another of electrically conductive pads 10 isconnected to an associated electrically conductive pad 12 using a solderstructure.

FIG. 5A depicts a first alternative to FIG. 4 illustrating across-sectional view of an electrical structure 2E, in accordance withembodiments of the present invention. In contrast with electricalstructure 2D of FIG. 4, electrical structure 2E of FIG. 5A comprises aplurality of interconnect structures 21. Each of interconnect structures21 comprises a non-solder metallic core structure 24 a, a non-soldermetallic core structure 24 b, and solder structure 5. Additionally(i.e., optionally), electrical structure 2E comprises an underfillencapsulant layer 16 comprising a first underfill encapsulant layer 16 aand a second underfill encapsulant layer 16 b. Alternatively, underfillencapsulant layer 16 may consist of only a single encapsulant layer.Each non-solder metallic core structure 24 a is thermo-compressionbonded to an associated electrically conductive pad 10. Each non-soldermetallic core structure 24 a is thermo-compression bonded to anassociated non-solder metallic core structure 24 b resulting in anelectrical and mechanical connection between each non-solder metalliccore structure 24 a to an associated a non-solder metallic corestructure 24 b. Each solder structure 5 electrically and mechanicallyconnects a non-solder metallic core structure 24 b to an associatedelectrically conductive pad 12. The aforementioned connections result ineach interconnect structure 21 electrically and mechanically connectingan electrically conductive pad 10 to an associated electricallyconductive pad 12. As with each non-solder metallic core structure 17 ofFIG. 3, each non-solder metallic core structure 24 a and 24 b of FIG. 5Amay comprise a first metallic material such as, inter alia, gold thatcompletely surrounds an exterior surface of a core comprising a secondnon-solder metallic material such as, inter alia, copper. Additionally,each non-solder metallic core structure 21 a and 21 b may comprise anadditional layer(s) of metallic materials surrounding non-soldermetallic core structure 24 a and 24 b. Additional layer(s) may compriseany conductive metallic material including, inter alia, nickel, gold,tin, etc. Underfill encapsulant layer 16 a surrounds non-solder metalliccore structures 21 a and is in contact with substrate 1. Underfillencapsulant layer 16 b surrounds non-solder metallic core structures 21b and is in contact with substrate 4. Underfill encapsulant layer 16 ais in contact with underfill encapsulant layer 16 b. Underfillencapsulant layer 16 a may comprise a first material (e.g., a highlyfilled silica-epoxy composite adhesive) and underfill encapsulant layer16 b may comprise a second and different material (e.g., a lightlyfilled silica-epoxy composite adhesive). Underfill encapsulant layer 16a may comprise a first coefficient of thermal expansion (e.g.,comprising a range of about 5-15 ppm/C) that is different (e.g., lower)from a second coefficient of thermal expansion (e.g., comprising a rangeof about 15-40 ppm/C) comprised by encapsulant layer 16 b. Underfillencapsulent layer 16 a may additionally comprise a filler 16 c dispersedthroughout.

FIG. 5B depicts a first alternative to FIG. 5A illustrating across-sectional view of an electrical structure 2F, in accordance withembodiments of the present invention. In contrast with electricalstructure 2E of FIG. 5A, electrical structure 2F of FIG. 5B comprisesinterconnect structures 21 a comprising a plurality of solder structures5 a electrically and mechanically connecting each non-solder metalliccore structure 24 a to an associated non-solder metallic core structure24 b.

FIG. 6A depicts a second alternative to FIG. 5A illustrating across-sectional view of an electrical structure 2G, in accordance withembodiments of the present invention. In contrast with electricalstructure 2E of FIG. 5A, electrical structure 2G of FIG. 6A comprisesinterconnect structures 21 b wherein each non-solder metallic corestructure 24 a of electrical structure 2G is thermo-compression bondedto an associated electrically conductive pad 12.

FIG. 6B depicts a first alternative to FIG. 6A illustrating across-sectional view of an electrical structure 2H, in accordance withembodiments of the present invention. In contrast with electricalstructure 2G of FIG. 6A, electrical structure 2H of FIG. 6B comprisesinterconnect structures 21 c comprising a plurality of solder structures5 a electrically and mechanically connecting each non-solder metalliccore structure 24 a to an associated non-solder metallic core structure24 b.

FIGS. 7A-7G illustrate a process for generating electrical structure 2Cof FIG. 3 and/or electrical structure 2D of FIG. 4, in accordance withembodiments of the present invention.

FIG. 7A illustrates a cross sectional view of substrate 1, in accordancewith embodiments of the present invention. Substrate 1 compriseselectrically conductive pads 10.

FIG. 7B illustrates a cross sectional view of a transfer substrate 43comprising a plurality of non-solder metallic core structures 17 a, inaccordance with embodiments of the present invention. Non-soldermetallic core structures 17 are positioned in cavities 43 a withintransfer substrate 43. Each of cavities 43 a comprises similardimensions as non-solder metallic core structures 17 with cavitypositions corresponding to positions of associated electricallyconductive pads 10 (i.e., from FIG. 7A). Transfer substrate 43 maycomprise, inter alia, glass, silicon, etc. Non-solder metallic corestructures 17 may be dispensed into cavities 43 a as a slurry in asolvent such as, inter alia, water alcohol (e.g., isopropanol), etc. Thesolvent may comprise an appropriate amount of flux (i.e., if generatingstructure 2D of FIG. 4) to assist in the wetting of solder structures 25(of FIG. 4) to non-solder metallic core structures 17 a. In a case inwhich non-solder metallic core structures 17 a are coated with a goldlayer 17 b, flux is not necessary. Optionally, the solvent mayadditionally comprise a small amount of thermally degradable polymericadhesive to aid in retaining non-solder metallic core structures 17 a incavities 43 a. Cavities 43 a are fabricated to a size that will onlycause one non-solder metallic core structure 17 a to fall into it duringa dispensing of non-solder metallic core structures 17 a.

FIG. 7C illustrates a cross sectional view of transfer substrate 43 ofFIG. 7D comprising a selected plurality of non-solder metallic corestructures 17 a, in accordance with embodiments of the presentinvention. As an optional feature of the process, transfer substrate 43may be covered with a polymeric film (i.e., not shown) withthrough-holes matching a pre-determined fraction of cavities 43 a. Thepre-determined fraction of cavities 43 a covered by the polymeric filmwill be prevented from receiving non-solder metallic core structures 17a. The pre-determined fraction of cavities 43 a allows a packagingdesign engineer to selectively place non-solder metallic core structures17 a. Additionally, solder interconnects or any other type ofinterconnect (i.e., not shown) may be selectively placed in some ofcavities 43 a (i.e., instead of select non-solder metallic corestructures 17) for placement on substrate 1. In this option, transfersubstrate 43 may be covered with a second polymeric film (i.e., notshown) with through-holes matching the remaining cavities 43 a. Thecavities 43 a covered by the polymeric film will be prevented fromreceiving solder interconnects.

FIG. 7D illustrates a cross sectional view of substrate 1 of FIG. 7Apositioned over transfer substrate 43 comprising non-solder metalliccore structures 17 a, in accordance with embodiments of the presentinvention. Substrate 1 of FIG. 7A is positioned over transfer substrate43 comprising non-solder metallic core structures 17 a in order totransfer non-solder metallic core structures 17 a to substrate 1.

FIG. 7E illustrates a cross sectional view of a structure 23 acomprising substrate 1 after non-solder metallic core structures 17 ahave been released from transfer substrate 43 and thermo-compressionbonded to electrically conductive pads 10, in accordance withembodiments of the present invention.

FIG. 7F illustrates a cross sectional view of structure 23 a positionedover substrate 4 comprising solder structures 25 of FIG. 4, inaccordance with embodiments of the present invention. Structure 23 a ispositioned over substrate 4 comprising solder structures 25 in order toform structure 2D of FIG. 4. Structure 2D of FIG. 4 comprisesthermo-compression bonds to electrically conductive pads 10 on substrate1 and solder connections to electrically conductive pads 12 on substrate4.

FIG. 7G depicts an alternative to FIG. 7F illustrating a cross sectionalview of structure 23 a positioned over substrate 4 of FIG. 3, inaccordance with embodiments of the present invention. Structure 23 a ispositioned over substrate 4 in order to form structure 2C of FIG. 3.Structure 2C of FIG. 3 comprises thermo-compression bonds toelectrically conductive pads 10 on substrate 1 and electricallyconductive pads 12 on substrate 4.

FIG. 7H depicts an alternative to FIG. 7G illustrating a cross sectionalview of structure 23 a positioned over substrate 4 of FIG. 3, inaccordance with embodiments of the present invention. In contrast withFIG. 7G, FIG. 7H illustrates optional underfill encapsulant layer 16.

FIGS. 8A-8E illustrate a process for generating electrical structure 2Aof FIG. 1 and/or electrical structure 2B of FIG. 2, in accordance withembodiments of the present invention.

FIG. 8A illustrates a cross sectional view of a structure 40 acomprising a sacrificial carrier substrate 35, a release layer 36, and aseed layer 37, in accordance with embodiments of the present invention.Sacrificial carrier substrate 35 may comprise any substrate materialincluding, inter alia, silicon, glass, etc. In order to form structure40 a, seed layer 37 (e.g., a blanket polymer layer such as, inter alia,a polyimide release layer) is applied to sacrificial carrier substrate35 and a seed layer 37 (e.g., copper, chromium, etc.) is applied overrelease layer 36. A photo resist layer (i.e., not shown) may be appliedover seed layer 37. The photo resist layer is patterned to forminterconnect structures 5 in FIG. 8B. A width for each of interconnectstructures selected from a range of about of 10-100 microns with anaspect ratio selected from a range of about 1:1 to 5:1. Interconnectstructures 5 may be formed by electroplating of vapor deposition andsubsequent chemical/mechanical polishing to insure a flat topography.Alternatively interconnect structures 5 may be formed by a subtractiveetch process in which a thick (e.g., 50 -100 um) copper layer is appliedto seed layer 37 by plating or bonding. The Copper layer would then becoated with photo resist, exposed with an I/O pattern, and subtractiveetched down to release layer 36. After removal of the photo resist,interconnect structures 5 may be filled with dielectric or under filladhesive. A surface of interconnect structures 5 is then planerized insuch a way to allow 0.1-1 um of copper protruding above a surface ofunderfill layer 16 of FIG. 8B. The Copper surface may be bonded directlyto electrically conductive pads 10 (see FIG. 8C) or a thin Au or Ni/Aulayer 5 a may be added to improve interconnect properties.

FIG. 8B illustrates a cross sectional view of a structure 40 b, inaccordance with embodiments of the present invention. Structure 40 b hasbeen formed from structure 40 of FIG. 8A.

FIG. 8C illustrates a cross sectional view of substrate 1, in accordancewith embodiments of the present invention. Substrate 1 compriseselectrically conductive pads 10.

FIG. 8D illustrates a cross sectional view of structure 40 b of FIG. 8Baligned over substrate 1 of FIG. 8C, in accordance with embodiments ofthe present invention. Structure 40 b is aligned over substrate 1 sothat interconnect structures may be thermo-compression bonded toelectrically conductive pads 10 in order to form structure 40C of FIG.8E. The alignment may be performed using bonding tools by direct viewingthrough the carrier via infrared or visible light.

FIG. 8E illustrates a cross sectional view of a structure 40C formedafter a thermo-compression bonding process and a removal of sacrificialcarrier substrate 35 layer a release layer 36 process has beenperformed, in accordance with embodiments of the present invention. Thetransfer process comprises heating the aligned assembly (i.e., from FIG.8D) to a temperature of between about 200 Celsius (C) to about 400 C.The heating process is performed at an inert atmosphere comprising apressure of 10-100 psi for 5 to 60 minutes. Optional layer of adhesive22 may be used to enhance a mechanical stability of structure 40C. Afterthe thermo-compression bonding process has been completed, sacrificialcarrier substrate 35 may be removed by laser ablation of release layer36 or by mechanical grinding and etching. Structure 40C is aligned oversubstrate 4 (i.e., of FIG. 1 or 2) and bonded to substrate 4 in order toform structure 2 a of FIG. 1 or structure 2 b of FIG. 2.

FIGS. 9A-9E illustrate a process for generating electrical structure2E-2H of FIGS. 5A-6B, in accordance with embodiments of the presentinvention.

FIG. 9A illustrates a cross sectional view of structure 23 b that issimilar to structure 23 a of FIG. 7E after underfill layer 16 a has beenformed, in accordance with embodiments of the present invention.Underfill layer 16 a may be applied at wafer-level or on singulateddevices. Wafer level underfill may contain a filler 16 c for lowcoefficient of thermal expansion (CTE). As an alternative, each ofnon-solder metallic core structures 24 a could comprise associatedsolder structures 5 a formed over a portion 33 of non-solder metalliccore structures 24 a. The aforementioned solder structures 5 a would beused to form structure 2F of FIG. 5B and structure 2H of FIG. 6B.

FIG. 9B illustrates a cross sectional view of a transfer substrate 43 acomprising a plurality of non-solder metallic core structures 24 b, inaccordance with embodiments of the present invention. Non-soldermetallic core structures 24 b are positioned in cavities 43 b withintransfer substrate 43 a. Each of cavities 43 b comprises similardimensions as non-solder metallic core structures 24 b with cavitypositions corresponding to positions of associated non-solder metalliccore structures 24 a (i.e., from FIG. 9A). Transfer substrate 43 a maycomprise, inter alia, glass, silicon, etc. Non-solder metallic corestructures 24 b may be dispensed into cavities 43 b as a slurry in asolvent such as, inter alia, water alcohol (e.g., isopropanol), etc. Thesolvent may comprise an appropriate amount of flux (i.e., if generatingstructure 2F of FIG. 5B or FIG. 2H of FIG. 6B) to assist in the wettingof solder structures 5 a (of FIGS. 5B and 6B) to non-solder metalliccore structures 24 a. In a case in which non-solder metallic corestructures 17 are coated with a gold layer, flux is not necessary.Optionally, the solvent may additionally comprise a small amount ofthermally degradable polymeric adhesive to aid in retaining non-soldermetallic core structures 24 b in cavities 43 b. Cavities 43 b arefabricated to a size that will only cause one non-solder metallic corestructure 24 b to fall into it during a dispensing of non-soldermetallic core structures 24 b.

FIG. 9C illustrates a cross sectional view of a structure 23 a of FIG.11A positioned over transfer substrate 43 a comprising non-soldermetallic core structures 24 a, in accordance with embodiments of thepresent invention. Structure 23 a of FIG. 11A is positioned overtransfer substrate 43 a comprising non-solder metallic core structures24 b in order to transfer and connect non-solder metallic corestructures 24 a to non-solder metallic core structures 24 b. Non-soldermetallic core structures 24 a are thermo-compression bonded tonon-solder metallic core structures 24 b to form structure 2E of FIG. 5Aand structure 2G of FIG. 6A. As an alternative, each of non-soldermetallic core structures 24 a could comprise associated solderstructures 5 a formed over a portion 33 of non-solder metallic corestructures 24 a. The aforementioned solder structures 5 a would be usedconnect non-solder metallic core structures 24 a to non-solder metalliccore structures 24 b in order to form structure 2F of FIG. 5B andstructure 2H of FIG. 6B.

FIG. 9D illustrates a cross sectional view of structure 23 a of FIG. 11Aafter non-solder metallic core structures 24 b have been connected tonon-solder metallic core structures 24 a, in accordance with embodimentsof the present invention. FIG. 9D illustrates a thermo-compression bondbetween non-solder metallic core structures 24 b and non-solder metalliccore structures 24 a. Alternatively, each of non-solder metallic corestructures 24 a could comprise associated solder structures 5 a toconnect non-solder metallic core structures 24 a to non-solder metalliccore structures 24 b.

FIG. 9E depicts an alternative to FIG. 9B illustrating a cross sectionalview of a transfer substrate 43 b comprising non-solder metallic corestructures 24 a and non-solder metallic core structures 24 b, inaccordance with embodiments of the present invention. Non-soldermetallic core structures 24 a have been thermo-compression bonded to andnon-solder metallic core structures 24 b. Substrate 1 has beenpositioned over transfer substrate 43 b comprising non-solder metalliccore structures 24 a and 24 b so that non-solder metallic corestructures 24 a may be thermo-compression bonded to electricallyconductive pads 10 with the resulting structure 23 c illustrated in FIG.9G.

FIG. 9G depicts structure 23 c resulting from the process described withreference to FIG. 9F, in accordance with embodiments of the presentinvention.

While embodiments of the present invention have been described hereinfor purposes of illustration, many modifications and changes will becomeapparent to those skilled in the art. Accordingly, the appended claimsare intended to encompass all such modifications and changes as fallwithin the true spirit and scope of this invention.

1. An electrical structure comprising: a first substrate comprising afirst electrically conductive pad; a second substrate comprising asecond electrically conductive pad; and an interconnect structureelectrically and mechanically connecting said first electricallyconductive pad to said second electrically conductive pad, wherein saidinterconnect structure comprises a non-solder metallic core structureand a first solder structure in direct mechanical contact with a firstportion of said non-solder metallic core structure, wherein said firstsolder structure electrically and mechanically connects said firstportion of said non-solder metallic core structure to said firstelectrically conductive pad, and wherein a second portion of saidnon-solder metallic core structure is thermo-compression bonded to saidsecond electrically conductive pad.
 2. The electrical structure of claim1, wherein said non-solder metallic core structure comprises acylindrical shape.
 3. The electrical structure of claim 1, wherein saidnon-solder metallic core structure comprises a spherical shape.
 4. Theelectrical structure of claim 1, wherein said non-solder metallic corestructure comprises a metallic material selected from the groupconsisting of copper, nickel, and gold.
 5. The electrical structure ofclaim 1, wherein said non-solder metallic core structure comprises afirst metallic structure and a second metallic structure covering and indirect mechanical contact with an entire exterior surface of said firstmetallic structure, wherein said second metallic structure completelysurrounds said first metallic structure, wherein said first metallicstructure comprises a first metallic material, wherein said secondmetallic structure comprises a second metallic material that differsfrom the first metallic material, wherein said first portion of saidnon-solder metallic core structure is located on said second metallicstructure, and wherein said second portion of said non-solder metalliccore structure is located on second metallic structure.
 6. Theelectrical structure of claim 1, wherein said interconnect structurecomprises a second solder structure, wherein said non-solder metalliccore structure comprises a first non-solder metallic core comprising aspherical shape and a second non-solder metallic core comprising saidspherical shape, wherein said second solder structure electrically andmechanically attaches said first non-solder metallic core to said secondnon-solder metallic core, wherein said first portion of said non-soldermetallic core structure is located on said first non-solder metalliccore, and wherein said second portion of said non-solder metallic corestructure is located on said second non-solder metallic core.
 7. Theelectrical structure of claim 6, wherein said first solder structurecomprises a first solder material, wherein said second solder structurecomprises a second solder material, and wherein said first soldermaterial differs from said second solder material.
 8. The electricalstructure of claim 6, further comprising: a first layer of underfillencapsulant surrounding said first non-solder metallic core and incontact with said first substrate; and a second layer of underfillencapsulant surrounding said second non-solder metallic core and incontact with said second substrate, wherein said first layer comprises afirst coefficient of thermal expansion, wherein said second layercomprises a second coefficient of thermal expansion, and wherein saidfirst coefficient of thermal expansion differs from said secondcoefficient of thermal expansion.
 9. The electrical structure of claim8, wherein said first substrate is a chip carrier, wherein said secondsubstrate is a semiconductor device.
 10. The electrical structure ofclaim 1, further comprising: a solder interconnect structure consistingof solder, wherein said first substrate comprises a third electricallyconductive pad, wherein said second substrate comprises a fourthelectrically conductive pad, and wherein said solder interconnectstructure electrically and mechanically connects said third electricallyconductive pad to said fourth electrically conductive pad.
 11. Theelectrical structure of claim 1, further comprising: a first layer ofwafer level underfill encapsulant surrounding said interconnectstructure and filling a space between said first substrate and saidsecond substrate. interconnect structure.
 12. The electrical structureof claim 1, wherein said non-solder metallic core structure comprises afirst non-solder metallic core comprising a spherical shape and a secondnon-solder metallic core comprising said spherical shape, wherein afirst non-solder metallic core is thermo-compression bonded to saidsecond non-solder metallic core, wherein said first portion of saidnon-solder metallic core structure is located on said first non-soldermetallic core, and wherein said second portion of said non-soldermetallic core structure is located on said second non-solder metalliccore.
 13. The electrical structure of claim 1, wherein said interconnectstructure comprises a second solder structure, wherein said non-soldermetallic core structure comprises a first non-solder metallic corecomprising a spherical shape and a second non-solder metallic corecomprising said spherical shape, wherein said second solder structureelectrically and mechanically attaches said first non-solder metalliccore to said second non-solder metallic core, wherein said first portionof said non-solder metallic core structure is located on said firstnon-solder metallic core, and wherein said second portion of saidnon-solder metallic core structure is located on said second non-soldermetallic core.
 14. The electrical structure of claim 13, wherein saidfirst non-solder metallic core comprises gold, and wherein said secondnon-solder metallic core comprises copper.
 15. The electrical structureof claim 13, further comprising: a first layer of underfill encapsulantsurrounding said first non-solder metallic core and in contact with saidfirst substrate; and a second layer of underfill encapsulant surroundingsaid second non-solder metallic core and in contact with said secondsubstrate, wherein said first layer comprises a first coefficient ofthermal expansion, wherein said second layer comprises a secondcoefficient of thermal expansion, and wherein said first coefficient ofthermal expansion differs from said second coefficient of thermalexpansion.
 16. The electrical structure of claim 1, further comprising:a solder interconnect structure consisting of solder, wherein said firstsubstrate comprises a third electrically conductive pad, wherein saidsecond substrate comprises a fourth electrically conductive pad, andwherein said solder interconnect structure electrically and mechanicallyconnects said third electrically conductive pad to said fourthelectrically conductive pad.
 17. The electrical structure of claim 1,wherein said non-solder metallic core structure comprises a firstnon-solder metallic core comprising a spherical shape and a secondnon-solder metallic core comprising said spherical shape, wherein afirst non-solder metallic core is thermo-compression bonded to saidsecond non-solder metallic core, wherein said first portion of saidnon-solder metallic core structure is located on said first non-soldermetallic core, and wherein said second portion of said non-soldermetallic core structure is located on said second non-solder metalliccore.
 18. The electrical structure of claim 1, wherein said firstelectrically conductive pad is formed within said first substrate,wherein said first electrically conductive pad comprises a firstmaterial layer formed over and in contact with a second material layer,wherein said first material layer comprises a different material fromsaid second material layer, wherein said second electrically conductivepad is formed within said second substrate, wherein said secondelectrically conductive pad comprises a third material layer formed overand in contact with a fourth material layer, and wherein said thirdmaterial layer comprises a different material from said fourth materiallayer.
 19. The electrical structure of claim 18, wherein said firstmaterial layer comprises a same material as said non-solder metalliccore structure.
 20. The electrical structure of claim 18, wherein saidthird material layer comprises a same material as said non-soldermetallic core structure.